University of Bath Reviews Olivier-Conklin DFT(tm) Method

University of Bath Reviews
Olivier-Conklin DFT(tm) Method

Dr. Tim Mays gives the new program high marks for its sophisticated scientific modeling, calculations and wide applicability.

At the University of Bath in Bath, England, Dr. Tim Mays of the School of Materials Science performs fundamental research characterizing surfaces and pores in solids using different experimental methods, such as gas transport, microscopy, and adsorption isotherms. He is particularly interested in the development of innovative mathematical, statistical, and numerical techniques for analyzing data from these experimental methods. The results are used to estimate characteristic functions such as pore size and surface energy distributions.

He first started working with molecular models of adsorption in the late 1980's as part of an ongoing research effort to develop new methods for interpreting isotherm data. Working in collaboration with Professor Brian McEnaney, who heads the School of Materials Science at Bath, Dr. Mays has developed applications for molecular models of adsorption in relation to melt-spun, pitch-based carbon fibers.

These fibers, supplied by Professor Dan Edie of Clemson University in Clemson, SC, are an ideal material for this type of analysis "because it is possible to control all stages of processing, from selection of the original pitch through to activation conditions," says Dr. Mays. "And second, the fibers do not have significant external or open macropore surface areas so that these do not have to be accounted for in analyses that consider only open pores smaller than about 50 nm," he added.

DFT Out-Performs Older Techniques

Of all the analysis techniques included with the Micromeritics' ASAP 2000 measurement system, Dr. Mays favors the Olivier-Conklin DFT(tm) program. Although the standard techniques are useful, he says, "There's no absolute answer to these things so it's useful to compare various techniques."

When comparing the Olivier-Conklin DFT method with the Horvath-Kawazoe method, Dr. Mays says, "To some extent the [Olivier-Conklin] DFT supersedes Horvath-Kawazoe because the basis of the development of the DFT is much more scientific and much more widely applicable than Horvath-Kawazoe. The Horvath-Kawazoe looks reasonable, but you're not sure how valid the results are."

Similarly, Dr. Mays thinks that although the Dubinin methods have been used for many years to obtain pore size distributions, Dubinin offers only a semi-empirical approach and attracts many scientific criticisms.

When comparing all the commercially available methods, Dr. Mays finds the Olivier-Conklin DFT method offers a significant advantage. He says, "The output of the [Olivier-Conklin] DFT method and similar approaches is probably the most scientific way to estimate pore size distributions of all the currently available methods. The model that's used to generate this method employs the most up-to-date scientific theories and calculations available. Also, the mathematical modeling behind it (DFT) is the most sophisticated. So, inevitably one tends to believe the results of DFT compared with other methods."

It took a lot of hard work to develop the Olivier-Conklin DFT program, but the effort has paid off. The DFT method offers a unified approach to analyzing the entire adsorption isotherm from beginning to end. It reports the complete pore size distribution for a given sample with seamless transitions between micropores, mesopores, and macropores. This kind of wide-scale applicability, combined with the fact that the DFT analysis uses a single molecular-based model built from up-to-date scientific calculations, means the DFT approach will likely turn into a worldwide standard for measuring pore size distributions.

As more and more people discover the DFT solution, the number of applications will multiply. Already, there is a need for pore models based on cylinders, says Dr. Mays. And in the future, he predicts demand will lead to automatic optimal smoothing methods, a wide range of adsorptive systems (such as nitrogen at temperatures other than 77 K, methane, carbon dioxide, and others), use of specialty adsorbents such as zeolites and microporous oxides, and other features that account for structural defects or contaminants on the adsorbent surface.